If you want to give your D&D character a tie to the divine and a chance to gain benefits (both roleplaying and mechanical) from worshiping a deity, an ideal, or a cause, then Complete Champion is a great book to use. As the introduction to the book mentions, your character doesn't have to sacrifice at a temple or give up doing what he likes to do best -- after all, the D&D game is about coming up with interesting ways to have fun. Complete Champion turns the myths and legends of the D&D game into usable features of the campaign world and shows you how to make them work best for your character.
Sample Holy Quests
Though almost any adventure can be considered a holy mission if its goals align with the interests of a church or deity, a true holy quest should have a much stronger and more central religious connection. Such quests can be broad and world-shaking, with enough scope to drive an entire campaign, or they might be relatively unimportant except for ceremonial purposes. They might be specific to a particular deity, or they might attract the attention of multiple divinities. For all their differences, however, all holy quests can bring champions the favor -- or the eternal ire -- of their deities and their churches.
The following sample quests demonstrate the breadth and diversity possible in the design of holy quests.
The Elemental Wellsprings
Scattered throughout the world, hidden from all but the greatest magic and the most learned sages, stand nexuses of elemental power. Each such place is devoted to one of the four elements (air, earth, fire, or water) and provides a conduit from its associated elemental plane to the Material Plane. These sites are the linchpins that hold the Material Plane in the center of the Inner Planes and allow all four elements to hold equal sway.
For several years, kingdoms and communities at the edges of the world's great deserts have noticed a slow but steady influx of refugees from the wastes. These stragglers report that crop failures have become commonplace in the border communities, and their few fertile fields have dried up and been swept under by the encroaching sands. The edges of the desert are creeping forward at impossible speed, sometimes moving visibly between one night and the next. The conclusion is clear -- the balance of elemental power in the world has shifted precariously to favor fire.
Led by fiends and creatures of elemental fire loyal to the Elemental Prince Imix, an army of monsters has located no fewer than half a dozen elemental wellsprings of water. Through a foul rite involving the fiery sacrifice of sentient beings and creatures of water, three of those wells have been corrupted, and their conduits have been broken and reshaped to draw upon the Elemental Plane of Fire. Even now, the forces of Imix are marching on the remaining three wells. If they are not stopped and the corrupted wells restored, the world will grow ever hotter, and its creatures ever more subservient to fire.
Druids and clerics of Obad-Hai and Ehlonna are fully aware of the danger. They seek champions -- preferably of their own churches, but any willing characters will do -- to seek out the six wells, protect the remaining three, and find some way of restoring the others.
Deities and Domains
This holy quest is of world-altering import. Most deities -- even evil ones -- would prefer that the realm of mortals not be destroyed by famine, drought, heat, and flame. Followers of the nature gods are especially determined to see the natural order set right, but any deity wishing to preserve its mortal following has a stake in the outcome. The deities most likely to send their own champions into the fray are those whose areas of interest include the Animal, Fire, Healing, Plant, Protection, and Water domains.
Animal: The animals of the world suffer as much as humanoids when the deserts expand and the fertile lands fade -- perhaps even more, since they lack access to technological and magical means of survival. Not only should adherents of the Animal domain seek to protect these creatures, but they can also make use of their connection with the beasts to help locate the enemy and the elemental wellsprings. From the animals, they can find out where the land first began to die, and what areas the animals avoid for fear of the alien and deadly creatures that now dwell there. Those who commune with animals also have spies and scouts who can lead them where they must go.
Fire: One might expect followers of fire to support the spread of their element, and indeed some do. But others know from holy writ or personal experience that fire out of control is to be feared rather than revered. Thus, they strive as hard as any to see the world put to rights, so that the power of the flame can once again be brought under their deities' influence. Clerics of fire can force the obedience of elementals, which might prove instrumental in the acquisition of information.
Healing: The people who have suffered, and the land itself, must be healed. Beasts of fire and fiends of the Lower Planes are anathema to life, so those who revere healing must stop them. Deities that offer the Healing domain do not consider it sufficient that their champions simply halt the destruction; they must find a way to undo it.
Plant: Plants as well as animals die when the desert spreads. Deities of plants and woodlands know that the encroachment of fire endangers not only the plants themselves, but ultimately every creature in the world that relies on any sort of food. Those who revere plants are willing to sacrifice animals or even people, if they must, if doing so could save this most basic building block of life and the environment.
Protection: Followers of protective deities care less about the specifics of what is happening and more about the end result -- people are suffering and dying. The threatened individuals and communities must be guarded at all costs. (This attitude does not extend to anyone who might be aiding the fiends and fire elementals in their activities.)
Water: Perhaps the most devoted and militant of all who strive against the spreading deserts are the followers of the water deities. They see a danger not only to the world, but also to the gods themselves, if this primary element of their divine portfolios weakens and fades from the world. For these champions, saving lives and communities is of secondary importance to restoring the elemental wellsprings and returning the four elements to a state of balance. Some zealous followers might seek retribution in the process, hoping to raise the element of water to prominence over the others.
For most characters, saving the world and gaining treasure from the potent enemies they face constitute sufficient reward. However, Obad-Hai, Ehlonna, and Yondalla have a direct stake in the completion of this mission. All three gods are grateful to have such devoted and potent servants on the Material Plane and are willing to take steps to keep them there. Any characters serving one of those deities who is slain in the course of a subsequent adventure is immediately subject to a reincarnate spell (PH 270), without the standard level loss or expensive material component. Each character can benefit from this blessing only once.